Study On The Mechanism Of White Rot Fungi Promoting Azo Dye Degradation

Synthetic dyes are essential in daily life, but problem of dye wastewater could not be ignored. White rot fungi was thought to degrade lignin by secreting ligninolytic enzymes in nature, and degrade synthetic dyes in similar way. It showed a broad prospect of dye wastewater treatment. It has been reported that white rot fungi grown in lignocellulose substrate could degrade pollutions more efficiently and lignin may play an important role in it. For research how lignin affect dye biodegradation and the mechanism in the process, co-substrate system with a variety of lignins and dye was constructed in this thesis, to find out whether lignin could stimulate dye biodegradation and reveal the possible principle.Firstly, we evaluated the lignin degradation ability of white rot fungi Echinodontium taxodii, which is good at degradating lignocellulose. Echinodontium taxodii could transform lignin into possible lignin degradation products in cultivating period. During the course laccase activity in extracellular fluid was influenced. Kraft Lignin(KL) had optimal promotion to laccase activity, which was 555.8% higher than the control group. Enzymatic/Mild-Acidolysis Lignin(EMAL) and Lignin Dehydrogenation Polymer(DHP) could enhance the laccase activity by 59.1% and 52.5% after added 4 days later. Mill Wood Lignin(MWL) had no effect on laccase activity.Secondly, we evaluated the degradating of azo dye DB38 by Echinodontium taxodii. Echinodontium taxodii cleaved the –N=N- linkage in the structure of DB38, then modified and transformed the products. In the final, DB38 had lower color degree and lower toxicity. Afterwards, four kinds of different lignin were added into the DB38 decoloration system to evaluate the effect of lignin in the co-substrate system respectively. KL and EMAL could obviously promote DB38 decolorization. EMAL was the better and its degradation kinetics constants k1=0.2362. Follwed by KL and its k1=0.2076. During the early period of dye degradation, the optimum promoted period, laccase activity was enhanced 386.79% and 160.19% by KL and EMAL.Choosing KL as research object studied its influence on DB38 degradation, because of its stimulating effect and practicality. High concentration KL in medium helped DB38 decolored more efficiently(500mg/L KL, k1=0.1504) while didn't increase the fungi biomass. And its stimulating effect didn't entirely depend on laccase activity. It means that lignin structure derivatives produced by KL in co-substrate system may promote dye biodegradetion. Therefore the higher KL concentration in medium, the quicker dye degraded. To prove whether the lignin structure derivatives consist in co-substrate system which produced from lignin could stimulate dye degradation, we conducted research of adding lignin structure derivatives into medium and apprasied their performance of improving dye decolorization. The results showed that vanillic acid, vanillin, homovanillic acid, acetovanillone and vanillyl alcohol could significantly increase the DB38 decolorization rate(vanillic acid is best, k1=0.2137).In conclusion, our study suggested that KL/EMAL and DB38 co-substrate system had optimal performance for dye biodegradation. The dye degradation enhancement may be resulted from lignin structure derivatives which generated in the course of lignin degradation. This thesis will contribute to the study of co-substrate theory and pollutions high-efficient bio-treatment.